1. Field of the Invention
The present invention relates to a functional substance (in the present invention, a substance that has an affinity to a target is called a functional substance) that shows a high affinity and/or high recognition specificity to various targets, is applicable to medicines, drug delivery, biosensors, control of gene expression level, overcoming of diseases due to gene defects, elucidation of functions of proteins translated by genes, development of reactive catalysts, etc., and is particularly favorable for analyzing and/or screening of proteins, as well as a method for producing the functional substance efficiently.
2. Description of the Related Art
With the development of bioscience, the focus of interest of researchers and scientists is shifting to analysis of proteins which are products by genes. The analysis of proteins is often performed through analysis of substances having affinities to individual proteins to be inspected.
Therefore, it is no exaggeration to say that the analysis of a protein is made possible only when there is a substance that has an affinity to the protein. Proteins to be analyzed are present in cells in a great variety and most of their amino-acid sequences, structures, etc. are quite unknown. Various substances are thus necessary in order to analyze proteins.
However, by now, efficient methods to produce or obtain such substances for analyzing proteins have not been sufficiently established. As the most general method for obtaining substances having affinities to specific proteins, methods to select affinity antibodies using animal immune systems are known. However, since these methods use animals, they require a large amount of proteins and numerous processing steps, and are accordingly costly. In addition, the affinity antibodies thus selected and obtained cannot be amplified (that is, reproduced). Also, there is a problem that only those which have an affinity to the same target are selected. Thus, it is extremely difficult to select individual affinity antibodies that have affinities to a great variety of proteins existing in cells, and obtain a sufficient amount of them.
Regarding the synthesis of proteins having gene information, there was a study in which puromycin was introduced into the 3′-terminal of an mRNA (Japanese Unexamined Patent Application Publication No. 2002-291491, claims, for example). This utilizes the property of puromycin being liable to be mistaken by a translation system as an amino acid and incorporated into a protein. However, the incorporation efficiency of puromycin has been rather low, and there have been only some reports in which functional substances have been selected from a library having random three amino acid residues.
On the other hand, as a method for identifying proteins using antibodies, the immunosensor amperometric method has been developed, for example. With this method, a tiny amount of proteins as small as about 2 ng/L can be measured. However, there are problems that almost all antibodies are not bound with proteins in a protein solution having such a low concentration, and that many non-specific reactions would occur in a solution (serum, for example) containing a lot of foreign substances, lowering the measurement accuracy.
In addition, although various proposals have been made including a supermolecule assembly that can coat viruses, etc. (Japanese Unexamined Patent Application Publication No. H10-508304, claims, for example), they have problems that the structures are complicated, and it is not possible to efficiently produce substances having affinities to many targets that are higher than those of antibodies.
There is a manufacturing method in which a mixture is synthesized that has numerous candidates for a substance having an affinity to a target, each in an extremely tiny amount; a substance that has an affinity to the target is selected from the substance candidates; the selected substance is then amplified in one way or another; the structure is analyzed using the amplified substance; and the substance for the purpose is selectively synthesized, based on the analyzed structure (Japanese Unexamined Patent Application Publication No. 2004-337022, paragraph number [0040], for example).
When a case is taken for an example in which the target is a protein, and a substance having a function such as described above is a nucleotide sequence, a mixture is synthesized that has numerous nucleotide sequences as candidates; a nucleotide sequence that has an affinity to a target protein is selected from among the numerous nucleotide sequences; it is amplified; the base sequence of this amplified nucleotide sequence is then determined; and the nucleotide sequence having an affinity to the target protein is produced, based on the determined sequence (that is, the determined structure).
In this way, it is possible to determine a functional substance for the purpose from among a tiny amount of functional substance candidates, and to realize its production. Accordingly, it is possible to quickly develop a sufficient amount of a novel functional substance.
If a sufficient amount of a functional substance is available, analysis of the structure of a target (sequence structure of a protein, for example), screening thereof, etc. can be developed by analyzing the structure, so that the result is applicable to medicines, drug delivery, biosensors, control of gene expression level, overcoming of diseases due to gene defects, elucidation of functions of proteins translated by genes, development of reactive catalysts, etc.
However, there is a problem that some of the selected functional substances cannot be amplified, and therefore, a sufficient amount of functional substances is not available. For example, while a PCR (Polymerase Chain Reaction) is often utilized in this amplification, some of the selected functional substances hinder the amplification by a PCR. When a selected functional substance has a strong positive charge or in a similar occasion, such hindrance occurs. If the amplification is hindered, it is not possible to determine the structure or produce the functional substance which are to be carried out after the amplification.
One of the causes is, for example, substituent groups introduced for the purpose of improving the affinity of functional substances to proteins that hinder the amplification reaction by a PCR or the like.